The present invention relates to an orthopedic implant having a porous surface and a method for making such an orthopedic implant.
The porous surface of the orthopedic implant is generally provided with a plurality of pores ranging in diameter between 10 and 500 microns. The bone tissues are thus capable of growing in the pores so as to unite the implant with the bone tissues. The conventional methods for making the implant with a porous surface include the plasma spray process, the sintering process, and the diffusion bonding process. The pores formed by the plasma spray process are not in communication with the outside, as shown in xe2x80x9cAxe2x80x9d, xe2x80x9cBxe2x80x9d, pores of FIG. 1. As a result, the bone tissues can not grow into them. On the other hand, they tend to form boundaries which are susceptible to breakage. The boundaries refer to the interfaces between the pores and the bone tissues. Similarly, the pores formed by the sintering process are not in communication with the outside and are susceptible to poor fatigue strength. As a result, the plasma spray process and the sintering process (either sintered beads or sintered fiber metal) can not be used to make the main structure of the orthopedic implant (Richard J. Friedman, et al., entitled xe2x80x9cCurrent Concepts in Orthopaedic Biomaterials and Implant Fixationxe2x80x9d, The Journal of Bone and Joint Surgery, Vol. 75-A, No. 7, July 1993). The diffusion bonding process, such as vapor deposition techniques for making the porous tantalum structure, can be used to make pores free from the drawbacks as described above [J. Dennis Bobyn, Michael Tanzer, and Jo E. Miller: Fundamental Principles of Biologic Fixation. In Morrey BF (ed): Reconstructive Surgery of The Joints. Churchill Livingstone, 1996, pp 75-94]. However, such porous structure has a relatively poor bending strength and is therefore vulnerable to deformation or damage by a bending force exerting thereon. Moreover, the porous titanium structure is not cost-effective.
It is the primary objective of the present invention to provide an orthopedic implant having a porous surface.
It is another objective of the present invention to provide an orthopedic implant having a pores-within-a-pore porous surface structure.
It is still another objective of the present invention to provide an orthopedic implant having a pores-within-a-pore porous surface structure, with a pore opening ranging in size between 10 and 800 microns.
It is still another objective of the present invention to provide a method for making an orthopedic implant having a porous surface.
The present invention provides an electrochemical technique employing a large electric current density and/or an intermediate electric current density for forming a pores-within-a-pore porous structure on a metal surface such that the porous structure is in communication with the outside, and that the porous structure is circumvented by a metal substrate. As a result, the porous structure is not vulnerable to boundary severance, poor fatigue strength and/or-bending.